[RAILS] Fix the `rake import:model:all` task to go through all models

[`reenable`](http://rake.rubyforge.org/classes/Rake/Task.html#M000115)
the "import:model" task after each invocation in "import:all".

 In order to ensure that any prerequisites that may be defined for the task being invoked in the loop,
 you would need to invoke on the first iteration and execute on future iterations. Reenable does it already.

 Closes #27